1. Field of the Invention
The present invention relates to a dielectric thin film device and a method for manufacturing the same. More particularly, the invention relates to a dielectric thin film device for use in non-volatile memory devices, capacitors, light modulation devices, piezoelectric devices and pyroelectric infrared rays sensors or the like, and a method for manufacturing the same.
2. Description of the Related Art
Generally speaking, capacitors comprising a dielectric thin film accumulate an electric charge in DRAM's or the like. As a material for the dielectric thin film for capacitors, SiO.sub.2 (silicon oxide) is primarily used. Furthermore, a higher integration of semiconductor device is demanded in recent years so that high dielectric thin films have been researched which use such materials as SrTiO.sub.3 (strontium titanate), (Ba, Sr) TiO.sub.3 (barium strontium titanate) or the like.
Also, non-volatile memories which use ferroelectric materials exhibiting a spontaneous polarization have been studied out of various kinds of dielectric materials. Examples of materials that can be used in such ferroelectric materials include oxides such as PZT [Pb(Zr, Ti)O.sub.3, lead zirconate titanate], PbTiO.sub.3 (lead titanate), and BaTiO.sub.3 (barium titanate) or the like. Out of such materials, PZT has been briskly studied as a promising material for non-volatile memories.
Along with the miniaturization and integration of electronic components resulting from an advancement of the semiconductor technology, dielectric thin film devices have reduced in size and thickness. Further demand has been made on dielectric thin films free from defects.
Methods for manufacturing dielectric thin films as mentioned above intend to utilize vacuum deposition method, sputtering method, sol-gel method, metal organic chemical vapor deposition (MOCVD) method or the like. The methods falls into two types; one type involving crystallization during the deposition of dielectric film forming process by raising temperature of substrate whereas the other type involving crystallization through heat treatment after the deposition of dielectric film. Both methods have a defect because when the dielectric thin film contains atom(s) that easily evaporates, many pin holes are formed in the dielectric thin film and uneven patterns on the surface thereof becomes larger due to reevaporation of volatile atom(s) during the crystallization. Thus, such dielectric thin film causes a problem that the leak current increases and the properties of cells get non-uniform. Consequently, it has been very difficult to thin down the thickness of the dielectric thin film along with the higher integration of semiconductor device.
In order to solve such problem, the former method raising temperature of substrate must maintain a high temperature of 500.degree. to 700.degree. C. for the substrate and slow down the rate of film formation which however lowers in productivity. In the latter method, when comparatively volatile atom(s) such as Pb or the like are used as dielectric materials, the film before heat treatment must be rich in Pb or the like so as to compensate a predetermined stoichiometric composition of the resulting dielectric film.
Besides, the ferroelectric thin film devices disclosed in Japanese Unexamined Patent Publication No. HEI 3-108192 and Japanese Unexamined Patent Publication No. HEI 3-108770 have a structure such that ferroelectric thin films constituting the device comprise a plurality of layers made different kinds of ferroelectric materials which may contain of a third atom. Such structures change a coercive field only to prevent a remnant polarization value from lowering, but they fail to prevent the formation of pin holes on the surface of dielectric thin films.